Peter Atherton, energy analyst at Liberum Capital, described price controls as a “Rubicon not to be crossed”.

But there was also dismay at Mr Miliband’s promise to seize undeveloped land from developers, halt the planned reduction in corporation tax, and raise the minimum wage. “Land taxes and energy price controls are not the answer” to Britain’s economic problems, the Institute of Directors said.

Mr Miliband’s warned that housebuilders who hold undeveloped land would have their property seized by a Labour government. In a stark ultimatum, the Labour leader said developers with land banks would have to “use it or lose it”. He promised that Labour would “dramatically increase housebuilding” with 200,000 new homes a year, every year during the next Parliament. “We will say to private developers you can’t just sit on land and refuse to build,” he said. “We’ll give them a very clear message, either use the land or lose the land.”

Stephen Stone, chief executive of Crest Nicholson, told The Daily Telegraph that Mr Miliband was “right to recognise that more housebuilding is needed.” But he warned that the policy idea was misguided. “It’s only land that will cost more to develop than sell that ever sits around,” he said. “It won’t make any difference if the government grabs it.”

Experts said the policy could hit companies beyond housebuilders. For instance, Tesco has one of the biggest land banks in Britain. The IoD said that the policy was “no substitute for simply making it easier to build.”

Leaders criticised Mr Miliband’s unashamedly left-wing speech as “anti-business” but some ideas were welcomed. The Federation of Small Business said the promised to reduce was “a step toward the fundamental reform the FSB has long sought.” The policy is likely to benefit big companies too. Sir Philip Green, the owner of Top Shop, has campaigned for a drop in business rates, pointing out that it is the biggest burden on retailers. Over 10 years Sir Philip says Arcadia has paid £1.3bn in rates compared to just under £600m in corporation tax.

Mr Miliband said the rates cut would be funded by scrapping the planned cut in headline corporation tax which is due to drop from 21pc to 20pc in April 2015. But the idea was strongly criticised by business leaders.

“Labour must realise that you can’t rob Peter to pay Paul,” said John Longworth, Director General at the British Chambers of Commerce. “The notion that you can offset cuts in one tax with changes to another doesn’t deal with the real problem.”

John Cridland the director general of the CBI agreed, telling the BBC that the policy damaged “Labour Party’s pro-enterprise credentials.”

Terry Scuoler, Chief Executive of EEF, the manufacturers’ organisation, said his members were alarmed by the threat to corporation tax which is “at odds with what our competitors are doing.” He said: “At a time when we are seeking to compete for every pound of investment, the headline rate of corporation tax sends an important signal to investors that Britain is open for business. Beyond its immediate impact, this will raise doubts amongst business on the commitment of a future Labour government to a competitive tax regime.”

The IoD’s Mr Walker the policy was “dangerous”. “The government has spent three years telling the world that we are open for business, and reductions in corporation tax have been a key part of that strategy,” he said. “It’s a dangerous move for Labour to risk our business-friendly environment in this way.”

George Bull, Baker Tilly’s Senior Tax Partner, said: “Although the business rates reduction will be welcomed by small firms, funding this move by scrapping a proposed reduction in corporation tax rates from 2015 is inconsistent with the policy of reducing corporation tax rates to boost businesses and improve the UK’s international competitiveness. If Labour is to abandon those goals, then it should come out and say so.”